Process of curing rubberlike materials



Patented July 26, 1949 "25171280 o PRoeEss -or oonmeitiiiifiiiitfikii 7 MATERIALS Francis PI Baldwin, I fluckemfin,N.'"J- .,'*assi g'fi0r to Standard Oil Development "Company, *a "corporation of Delaware No'Drawing. Application February-8, 194

-SEEMS/LNG. 5213563 "16 Claims. (crate-9417) This invention relates to synthetic rubber, relates particularly 'to the "curing f rubber-like polymers of isobutylene with a diolefin; and relates especially to means for reducing the-tendency toward scorchiness during the processing-of such polymers preparatoryto curing by thef-use of quinoid type of curin'g 'inate'rials.

It has been fou nd 'pos'sible'to copolymerize isoolefins :such as isobutylene with polyol'efins such as butadiene at low temperatures by the use of a dissolved Friedel-Craiits 'type'catalyst; to yield exceedingly valuable rubber-like copolymers which reactwith sulfur and with paraquinonedioxime in a curing reaction; which is in some ways analogous to the vulcanization'of rubber. When so cured these polymers yield exceedingly valuable rubber substitutes. which are characterized by high tensile strength, high modulus and other very valuable physical properties However, in the processing of these polymers difficulty is ex,- perienced due to the fact that they must be milled in order to incorporateinto them the various compounding agents and the curing agent and the necessary elevation of temperatureduring the compounding to incorporate the curing agent, often results in a premature curing reaction, identified :by the shop as scorchiness, Whichseriously inter-fer-eswith compounding, calendering, extruding and other processes, and'exerts various. other harmfuleffects during mold ing and curing. V

The curing of this copolyrner by the use of paraquinone "dioxins isjde'scr'ibed thfCO-Dnding 'aPDIiQatiQn Serial No. 426,71*5; filed7 January 14, 1942, now Patent" Number 2,393,321, in the nameof J; P.H1aworth;

The present invention provides a means for overcoming this. scorchiness by the 'additionto the copolymer of substances which 'wi'll, yield acids, or the acids the selves,particularly.suit} able being such substances as; lead benzoate and other lead and heavy meter salts which upon heating yield-ac dic; effects, or both a'cidijceifects n x zin fect These m rials are used; as compoundin agentsand added to the olymer compound before the clifih agent and sulfuriz'ation aid or accelerator aremixed in. The presence of the acidic body'pre'v'ents a premature reaction between the polymer and the curing agent under the influence of the vulcanization aid or accelerator.

Thus the inventio'nc onsists of a new composition of matter comprising broadly an isoolefihl fin nte o ymenand a.curing a ent, preferably paraquinone dioxi'rhe or its aryl'esters; in

admixture, with. a.,.'S'I 3 l lirbportionof. lead benzoate or other; lead or heavy'metal' salt or reasonably easy v dissociable acidic;compound-which, by its presence. er s; he: u pose: i avo d scorchin'ess-of'thepo- "er while itisbeing processed. "Other objects and'detalls of'the invention will be-apparentirom the following description:

The raw material to. which 'the present inventionz'isfappliecl'is a copolymer' of an isool'efin with a polyolefin. The preferredisoolefin is isobutylone, but'other-isoolefilis M5, 6, 7 and 8 or more carbon atoms per molecule are also usable-particularly flginethyl butene l 2griiethyl pentene-l, and 2,1i1ethyl heifenes li and "the like. For the polyolefin substantially any of 'th'e polyolefins suchaswbutadieiie; 'isopreiie, piperyl'ene, dimethyl butadienarnwrceiief hd 'tlielike having from four up to twelve of fourteen carbonatonis per molecule are.e=usefnl. In the.-' pifeparationof the polymer, the- 'isoolefiii *i'si d'esirabiy presen in major proportion with the qielyolefih present in minor proportion, mixtures having from -parts 'to 99 .5 parts-of *therisoclefin with 30 13 3 05 parts of the nolyolefinrbein'g -1:ireferred; flfhe olefinic mixture is advajntageoiisly cooled: to" temperatures within thehrange (if-about 2Q 'G 'to '100 'C. or even lower, to "=l659":, th preferred range being between soe-eziaria rial maybescooledrby fei'iigeratingjacket upon the-reactor,- utiiiziiig such; refrigerants a liquid ethylene; .l-iquid etli'ane "er Iii11iid.'-"niethahe ro'r the like, eithe'nat 'rfeeueea pifessfires or at superatmospherici pressuresaccording to the desired temperature.

Alternatively, internal refrigerants such as liquid ethylene on ;solid carbon dioxide or liquid ee' ereeliae dims ha may be used rectly in admixture with the olefinic material,

1 again reautea pressures or elevated pressure'stbeing useda'sdes'ireid M v The cold olefiniq material is polymerized by the application "thereto ofa Eriedel crafts cat- Tli'e'catalyst preferably a solid catalyst.

de in solutionin a low- 0; e; bein :thereby;lowireezingj" are 'useful' and it is characteristic of the alkyl halides 'that iior'f'ofiiplex aiming solvent; but

I e or thesolvent such substances as carbon -disulflde :or; its homologu'es 3 they, like carbon disulfide, form no complexes with the Friedel-Crafts catalysts.

The polymerization reaction is conveniently conducted by spraying the liquid catalyst solution onto the surface of the cold, rapidly stirred olefinic material; or the catalyst may be injected as a rapid stream into a zone of high turbulence in the olefinic material; or ,other convenient means for obtaining rapid dispersion of the catalyst solution into the olefinic mixture may be used. a

The polymerization reaction proceeds rapidly to yield a solid polymer and the reaction may be continued until from 60% to 90% of the olefinic material present is polymerized. When the reaction has reached the desired stage, the solid polymer is desirably separated from residual portions of the polymerization mixture and brought up to room temperature. A convenient method of accomplishing this is to dump the contents of the reactor into warm water, or into warm alkaline solution, or into warm alcohol solution, or the like.

The resulting polymer may then be washed on the mill, if desired or otherwise purified. The resulting polymer may have a molecular weight (as determined by the Staudinger viscosity method) of from 20,000'to 150,000, or above, the preferred molecular weight being from 40,000 to 80,000 The polymer mayalso show an iodine number (as determined by the Wijs method) of from 1 to 40 or 50, thepreferred range of iodine number being between 1 and about 10. This material thus is a high grade rubber substitute.

It is'found that this material cures readily with curing agents to yield; cured materials having tensile strengths ranging from 1,200 to 5,000 pounds per square inch with elongations ranging from 400% to 1200%, very high abrasion and flexure resistance, phenomenally high resistance to chemicals generally and solvents generally, except the petroleum hydrocarbons, and an excellent resistance to ultra violet light and to oxidation.

In preparing this polymer for use, it is con veniently compounded according to the following receipe:

' Parts by weight Polymer -1 100.0 Zinc oxide 3.0 Stearic acid 3.0 Thermatomic carbon black 50.0 Processing oil 10.0 p-Quinone dioxime 2.0 1 10304 10.0

However, when compounded according to this recipe, the material shows a very troublesome scorchiness to the extent that unless the utmost care is exercised and the material kept at the lowest possible temperaturev during processing,

the material may setup into a nearly complete cure on the mill during the compounding.

According to the present invention, this tendency toward premature curing or scorchiness is overcome by incorporating into the polymer the scorch preventative agent of the present invention, such as lead benzoate or lead salts of the aromatic acids in general such as lead salicylate, lead phthalate and the like, and other similar salts of other heavy metals such as tin, cadmium, and the like, including those metals low in the electromotive series; particularly those which ionize in water solution to produce a pH below about 7; or the corresponding, acids may be used as such.

EXAMPLE 1 A sample of polymer prepared as above described from isobutylene and isoprene containing approximately one molecular percent of isoprene, showing a molecular weight of approximately 45,000 and an iodine number of approximately 1.5 was compounded according to the following recipe:

Parts by weight Polymer 100.0 Zinc oxide 3.0 Stearic acid 3.0 Thermatomlc carbon. black 50.0 Petroleum oil 10.0

A low viscosity parafllnic pale oil, produced byconventional distillation and acid treatment, having the iol lowing specification curing agent consisting of a i .Parts by weight Quinone dioxime 2.0 Pb304 10.0

was milled in. Even'at this relatively low temperature the material was visibly scorched at the end of ten minutes and the material showed very troublesome signs of pres-curing, or scorchiness, to the extent that it was difiicult to mill,

difficult to calender, practically impossible to ex trude and difiicult to force into all the crevices of the mold.

The other portion was then further compounded with Pars-b weight Quinone dioxime 2.0 1 10304 L 10.0 Lead benzoate 2.0

This compound did not scorch on the" mill at 200 F. and showed no signs or scorch .in twenty minutes milling-yet it cured readily and. normally in the press at 287 F. with no noticeable change in curing properties or any othercharacteristics over the same compound containing no lead benzoate. r

The resulting cured material-showed a tensile strength slightly superior to the tensile strength of material containing no lead benzoate; showed approximately the same elongation at break and approximately the same flexure resistance and abrasion resistance. The Mooney plasticity of the material. after compounding and before curing was found to be considerably better because of the absence of scorchiness and absence ofany tendency towards precuring. r

A series of compounds were prepared according to the recipe shown inthefollowing Table 1, in which the left hand column shows the recipe, the first. column of .numbers'records the results of a control run, and the following six columns show the results of various amounts of various scorchiness preventers according to the present invention. The first nine lines of thetable. show the compounding recipe, and the lines below show the values for tensile strength, elongation and modulus at 300% of the several compounds after different lengths of time of curing at difi'erent temperatures.

It will be observed that these aromatic 001 s are substantially as good scorchiness preventers as are the lead salts of similar acids.

'Table 1 Control I II III IV V VI Pol er 100.0 100.0 100.0 21115 511100.-. 5. 0 5. 0 5. 0 Stearic Acid 6. 0 6. 0 6. 0 Carbon Black 64. 0 64. 0 64. 0 p-quinone rlioximn 2. 0 2. 0 2. 0 Pb304 10. 0 10. 0 10. 0 Lead Salicylatc I Lead Benzoate g 4. 0 Lead Phthalate 2.0 4. 0=

T 11 E1 .Mod. 300: g 1 1r gi 1 2 5'/22? :5. fn ?f -9; 1200050 710-980 530-1090 1330-710 1200-770 1320-030 1230-530 7 I 14610-640 1100 840 1010 890 1320 640 12% 600 132 0-640 500 I O Cured 40/227 F 540 210 180 520 440 600 1 Normal cures:

1180-480 1280-590 1150-570 1160-550 1170-560 1210-530 1110-480 WWW F .220... 1028 540 use... .02....

I O F mm .0 use... W .0 1.20... a...

I O MW F 0a. 0a.. 02a... 7 O F l I l l n I Cured 80 I287 570 560 450 490 440 540 670 It will be noted that when the compound is EXAMPLE 4 heated for or 40 minutes at 227 F., which is approximately compounding temperature, on the mill, less curing occurs when the lead salts are present, as shown in columns 2 to 7 inclusive,

A similar series of determinations were run with thiosalicylic acid according to the recipe shown in the following Table 3:

whereas the material is practically fully cured in Table 3 the absence of the scorchiness preventers, as shown by column 1. In addition, when the ma- Control I n terial is cured at 287 F.. there is very little difference in the resulting tensile strength, elongam0 m0 m0 0.0 5.0

tion and modulus between the compound of col steam acid 3.0 3.0 M umn 1 contalning no scorchiness preventers and O b l: at on black 54.0 54.0 54.0 the compounds 01 columns 2 to '7 inclusive, which flumone dionme 2' 0 2.0 2 0 contam the scorohines preventers. It W111 be ev1- tbaoh: mg 10.0 no dent from the test records shown in Table 1 that (0 Thimhcylic these three scorchiness preventers are highly efsm nsn fective for preventing precuring during comp v. Cured 20227F 1260-870 290-1100 -1100 pounding, and are without effect upon the cured b 280 material, cured at normal temperatures and cured /227 F 533 9 53 imes. 1 45 Cured 60/227F 12704-4580 830E370 250 20 EXAMPLE 3 Cured 107207 1200 00 9804-00070 1030 A similar series of compounds were prepared Cured 20/287"F ggg WOOQQO 53 utilizing for the scorchiness preventer a series Cured40'/287F 1270-680 1040-660 1020-720 of aromatic acids, as shown in the following Ta- 60 ble 2. These acids were used in the same way as the lead salts in Table 1, and they perform similar functions, as will be observed from the tensile strength and elongation data recorded in It will be observed that thiosalicylic acid likewise is about as efiective as a scorchiness preventer as the lead aromatic acid salts.

Table 2. 55 The above examples show the reaction with Table 2 Control I II III IV Polymer 100. 0 100. 0

Zinc Oxide 5.0 5.0

Stearic Acid 3. 0 3. 0

Semi-Reinforcing Furnace Black 54. 0 54. 0

Qulnone Dioxime 2. 0 2. 0

Pb301 l0. 0 10. 0

Benzoic Acid Salyclic Acid o-chlorbenzoic 2. 0

p-chlorbenzoic Acid Scorch Cures, Tensile-Elong.:

Cured 20/227F 1260-480 730-1000 0-l100+ 730-970 530-1000 Cured 40'/227F 1340-770 1070-800 310-950 1010-830 1010-790 Tensile-Mod. @800-Elong.:

Cured 10/287F 1180-450-050 980-480-610 1100-450-660 1040-500-650 1210-530-660 Cured 20/287F 1190-430-050 980-470-550 1070-530-640 970-460-630 1180-510-620 Cured 40/287F 1100-420-050 1100-540-620 950-490-630 970-430-690 1160-490-600 Cured 80/287F 1100-440-580 1140-550-600 900-510-000 1040-400-700 1130-450-650 venting agent, in the range between 0.5 parts and 4 parts per 100 parts of polymer, comprising a compound having an aromatic acid salt of lead.

6. A composition of matter comprising a rub bery polymer having polymerized thereinto isobutlylene and a significant amount of a multiolefin having from 4 to 14 inclusive carbon atoms per molecule in the monomer before polymerization; together with a curing agent in an amount on the order of magnitude of 2 parts per 100 parts of polymer, comprisin a compound having a quinone dioxime nucleus; and a scorchiness preventing agent, in the range between 0.5 part and 4 parts per 100 parts of polymer, comprising a compound having an aromatic acid salt of cadmium.

7. A composition of matter comprising a rubbery polymer having polymerized thereinto isobutylene and a significant amount of a multiolefin having from 4 to 14 inclusive carbon atoms per molecule in the monomer before polymerization; together with a curing agent, in an amount on the order of magnitude of 2 parts per 100 parts of polymer, comprising a compound having para quinone dioxime; and a scorchiness preventing agent, in the range between 0.5 part and 4 parts per 100 parts of polymer, comprising a compound having an aromatic acid salt of lead,

8. A composition of matter comprising a rub bery polymer havin polymerized thereinto isobutylene and a significant amount of a multiolefin having from 4 to 14 inclusive carbon atoms per molecule in the monomer before polymerization; together with a curing agent in an amount on the order of magnitude of 2 parts per 100 parts of polymer, comprising a compound having para ,quinone dioxime; and a scorchiness preventing agent, in the range between 0.5 part and 4 parts per 100 parts of polymer, comprising a compound having an aromatic acid salt of cadmium 9. In the processing of a rubbery polymer, the steps in combination of milling into the polymer from 0.5 part to 4 parts per 100 parts of polymer of a scorchiness preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus.

10. In the processing of a rubbery polymer, the steps in combination of milling into the polymer from 0.5 part to 4 parts per 100 parts of polymer of a scorchiness preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus, and thereafter heating the mixture to a curing temperature of the order of magnitude of 287 F.

11. In the processing of a rubbery polymer, comprising a polymer having polymerized thereinto a significant amount of a multi-olefin having from 4 to 14 inclusive carbon atoms per molecule in the monomer before polymerization, the steps in combination of milling into the elastomer from 0.5 part to 4 parts per 100 parts of elastomer of a scorchiness preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus.

12. In the processing or a. rubbery polymer, comprising a polymer having polymerized thereinto a significant amount of a multi-olefin having from 4 to 14 inclusive carbon atoms per molecule in the monomer before polymerization, the steps in combination of milling into the elastomer from 0.5 part to 4 arts per parts of elastomer of a scorchiness preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus, and thereafter heating the mixture to a curing temperature of the order of magnitude of 287 F.

13. In the processing of a rubbery polymer, comprising a copolymer of a major proportion of isobutylene with a minor proportion of a multi-olefin having from 4 to 14 carbon atoms per molecule, the steps in combination of millin into the elastomer from 0.5 part to 4 parts per 100 parts of elastomer of a scorchin-ess preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus.

14. In the processing of a rubbery polymer, comprising a copolymer of a major proportion of isobutylene with a minor proportion of a multiolefine having from 4 to 14 carbon atoms per molecule, the steps in combination of milling into the elastomer from 0.5 part to 4 parts per 100 parts of elastomer of a scorchiness preventing agent comprising a compound having an aromatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus, and thereafter heatin the mixture to a curing temperature of the order of magnitude of 287 F.

15. In the processing of a rubbery polymer, comprising a copolymer of a major proportion of isobutylene with a minor proportion of isoprene, the steps in combination of milling into the elastomer from 0.5 part to 4 parts per 100 parts of elastomer of a scorchiness preventing agent comprising a compound having an arcmatic acid nucleus; and an amount on the order of magnitude of two parts per 100 parts of elastomer of a curing agent comprising a compound having a quinone dioxime nucleus.

16. A composition of matter comprising a polymer having polymerized thereinto approximately 97.5 parts of isobutylene and approximately 2.5 parts of isoprene, together with a, curing agent comprising paraquinone dioxime in the proportion of approximately 2 parts by weight per hundred of polymer and 2 parts by Weight of lead peroxide, and a scorchiness-preventing agent comprising lead benzoate in the proportion between 0.5 part and 4 parts per hundred parts of polymer.

FRANCIS P. BALDWIN.

REFERENCES CITED The follolw-ingreferenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,170,191 Fisher Aug. 22, 1939 2,311,004 Thom-as Feb. 16, 1943 2,395,778 Breck Feb. 26, 1946 FOREIGN PATENTS Number Country Date 389,139 Great Britain Mar. 13, 1933 

